Sheet conveying apparatus and image forming apparatus

Abstract

A sheet conveying apparatus includes a sheet conveying unit including a drive roller and a driven roller; a downstream detection unit and an upstream detection unit; a conveying amount measuring unit that measures a conveying amount of the sheet; and a conveying distance calculation unit that calculates a conveying distance of the sheet, wherein a distance between the downstream detection unit and the upstream detection unit or a perimeter of one of the drive roller and the driven roller is set such that an expected conveying distance calculated based on a set sheet length of an expected value of the sheet becomes a substantially integer multiple of a perimeter of the one of the drive roller and the driven roller.

What is claimed is: 
     
       1. A sheet conveying apparatus comprising:
 a first roller and a second roller that convey a sheet along a conveying path of the sheet so that the sheet is inserted between the first roller and the second roller; 
 an upstream detection unit that detects the sheet upstream of the first roller and the second roller on the conveying path; 
 a downstream detection unit that detects the sheet downstream of the first roller and the second roller on the conveying path, 
 the downstream detection unit being positioned apart from the second roller for a distance longer than the distance necessary for a velocity turbulence of the second roller that is generated when the sheet is inserted between the first roller and the second roller to dissipate; 
 a conveying amount measuring unit that measures a conveying amount of the sheet conveyed by the first roller or the second roller; and 
 a conveying distance calculation unit that calculates a conveying distance of the sheet conveyed by the first roller and the second roller based on detected results by the upstream detection unit and the downstream detection unit and a measured result by the conveying amount measuring unit, 
 wherein a conveying distance of the sheet conveyed by the first roller and the second roller within a period between when the sheet is detected by the downstream detection unit and when the sheet is detected by the upstream detection unit is substantially an integer multiple of perimeter of the first roller. 
 
     
     
       2. The sheet conveying apparatus according to  claim 1 , further comprising:
 a plurality of at least either of the downstream detection units and the upstream detection units provided at different positions in a conveying direction of the sheet. 
 
     
     
       3. An image forming apparatus comprising:
 the sheet conveying apparatus according to  claim 1 ; and 
 a transfer unit that transfers a toner image onto the sheet. 
 
     
     
       4. A sheet conveying apparatus comprising:
 a first convey unit that includes
 a first roller, 
 a first drive unit that outputs a driving force to rotate the first roller at a first peripheral speed Va, 
 an one-way clutch that transmits the driving force output by the first drive unit to the first roller only in a direction that the first roller is rotated to convey a sheet in a conveying direction of the sheet, and 
 a second roller that is driven to rotate in accordance with the rotation of the first roller and convey the sheet with the first roller so that the sheet is inserted between the first roller and the second roller; and 
 
 a second convey unit that receives the sheet from the first convey unit and includes,
 a third roller that is rotated at a second peripheral speed Vb that is faster than or equal to the first peripheral speed Va, 
 a fourth roller that conveys the sheet along a conveying path of the sheet with the third roller, 
 a second drive unit that outputs a driving force to rotate the fourth roller at a third peripheral speed Vc that is faster than or equal to the second peripheral speed Vb, 
 a torque limiter that is provided between the second drive unit and the fourth roller, whose slip torque is set to be less than load torque generated when the third roller and the fourth roller are in contact with each other and stops transmitting the driving force from the second drive unit to the fourth roller when the third roller and the fourth roller are in contact with each other; 
 
 an upstream detection unit that detects the sheet upstream of the first roller and the second roller on the conveying path; 
 a downstream detection unit that detects the sheet downstream of the first roller and the second roller on the conveying path; 
 a conveying amount measuring unit that measures a conveying amount of the sheet conveyed by the first roller or the second roller; and 
 a conveying distance calculation unit that calculates a conveying distance of the sheet conveyed by the first roller and the second roller based on detected results by the upstream detection unit and the downstream detection unit and a measured result by the conveying amount measuring unit, 
 wherein a conveying distance of the sheet conveyed by the first roller and the second roller within a period between when the sheet is detected by the downstream detection unit and when the sheet is detected by the upstream detection unit is substantially an integer multiple of perimeter of the first roller. 
 
     
     
       5. An image forming apparatus comprising:
 the sheet conveying apparatus according to  claim 4 ; and 
 a transfer unit that transfers a toner image onto the sheet. 
 
     
     
       6. A sheet conveying apparatus comprising:
 a driver roller and a driven roller that convey a sheet along a conveying path of the sheet so that the sheet is inserted between the driver roller and the driven roller; 
 an upstream detection unit that detects the sheet upstream of the driver roller and the driven roller on the conveying path; 
 a downstream detection unit that detects the sheet downstream of the driver roller and the driven roller on the conveying path, 
 the downstream detection unit being positioned apart from the driven roller for a distance longer than the distance necessary for a velocity turbulence of the driven roller that is generated when the sheet is inserted between the drive roller and the driven roller to dissipate; and 
 a conveying amount measuring unit that measures a conveying amount of the sheet by counting a pulse signal of a rotary encoder provided at a rotation axle of the driver roller or the driven roller, 
 wherein a conveying distance of the sheet conveyed by the drive roller and the driven roller within a period between when the sheet is detected by the downstream detection unit and when the sheet is detected by the upstream detection unit is substantially an integer multiple of perimeter of the drive roller or the driven roller. 
 
     
     
       7. The sheet conveying apparatus according to  claim 6 , further comprising:
 a conveying distance calculation unit that calculates a conveying distance of the sheet conveyed based on a detected result by the upstream detection unit and the downstream detection unit and a measured result by the conveying amount measuring unit. 
 
     
     
       8. The sheet conveying apparatus according to  claim 6 ,
 wherein the distance between the downstream detection unit and the upstream detection unit is determined to be within a predetermined range based on a range of an allowable measurement error of the conveying amount measuring unit.